Secondary batteries such as lithium ion secondary batteries, which have characteristics such as compact size, light weight, high energy-density, and being rechargeable, are used in a wide variety of applications. Thereupon, in recent years, for the purpose of achieving higher performance of secondary batteries, studies have been made to improve battery members such as electrodes.
Here, battery members such as electrodes (active and negative electrodes) of a secondary battery and a porous membrane provided on the electrodes or a separator provided in order to improve the heat resistance and the strength are formed by binding together components contained in those battery members or binding those components and base members (for example, current collectors, electrodes, a separator, and the like) using a binder. Specifically, for example, a negative electrode of a secondary battery commonly includes a current collector and a negative electrode mix layer formed on the current collector. The negative electrode mix layer is formed, for example, by applying a slurry composition onto the current collector and drying the slurry composition thus binding the negative electrode active material and others using a binder. The slurry composition is obtained by dispersing for example a negative electrode active material and a binder composition in a dispersion medium.
Given this factor, in recent years, in order to achieve further improvement in the performance of secondary batteries, there have been attempts to improve binder compositions and slurry compositions used for the formation of those battery members.
Specifically, for example, there has been proposed to improve the performance of a secondary battery by blending a cross-linking agent with a binder composition or a slurry composition used for the formation of electrodes of the secondary battery, and forming electrodes using the binder composition and the slurry composition. For example, JP 2000-106189 A (PTL 1) proposes a secondary battery having a negative electrode comprising a mixture including a negative electrode active material, a binder, a thickener such as carboxymethyl cellulose, and at least one cross-linking agent selected from the group consisting of a melamine-based resin, a urea formalin resin, tannic acid, a glyoxal-based resin, a dimethylol compound, and PVA. Further, PTL 1 describes that for example carboxymethyl celluloses (thickeners) are cross-linked by a cross-linking agent.
For example, JP 2011-134618 A (PTL 2) proposes a binder composition for a secondary battery electrode, including functional-group-containing resin particles that are obtained by emulsion polymerizing ethylenic unsaturated monomers containing keto-group containing ethylenic unsaturated monomers and a multifunctional hydrazide compound as a cross-linking agent. Further, PTL 2 discloses that the functional group-containing resin particles are cross-linked by the multifunctional hydrazide compound.
For example, JP H11-288741 A (PTL 3) proposes a lithium ion secondary battery having a porous coating on at least one of a positive electrode and a negative electrode, in which the positive electrode or the negative electrode is formed using a binder including a water-soluble macromolecular material having a hydroxy group and a cross-linking agent having a functional group reacting with the hydroxy group. Further, PTL 3 describes that the water-soluble macromolecular materials are cross-linked by a cross-linking agent.